To fully appreciate the invention, one must understand the nature and operation of interlock mechanisms and their great importance to our heavily industrialized society. There is a constant and continuous need to work on industrial equipment in a quick and efficient manner without jeopardizing the safety of personnel. The present invention is directed to testing systems and mechanisms for ensuring the integrity of interlocks so that they will function correctly with the passage of time and without the need to open the guards or disrupt the operation of the machinery guarded by them. Interlocks may be any go not-go device, and they can be mechanical, electrical, electronic, electromagnetic, magnetic, pneumatic, hydraulic, etc., and their combinations.
To fully understand the various ramifications of applicant's novel testing system and to employ same, one must have a basic understanding of the way interlocks function and to provide this assistance, there are provided examples of various typical types of interlocks that have been modified, where necessary, to permit testing.
Generally speaking, all interlocks contain a sensor whose state is changed when a change of the relative positions of the interlock sensor and the guard it is acting on takes place such as by movement or the state of the sensor is changed when, through some means interposed between the sensor and the guard, the guarded space is accessed or breached. It is the change of state of the sensor that is utilized to change the operating state of the machine or to shut down the machinery posing the hazard in the guarded space.
For instance, if the interlock sensor is a normally open pushbutton switch which is kept closed by the guard then, when the guard is opened, the change of the relative position of the guard to the switch allows the pushbutton to spring open, causing the switch to change from the closed to the open state and thereby to change the operating state of the machine or turn off the machine.
Similarly, for example, if the guard and interlock system is a light curtain, the curtain of light beams serves as the guard and one or more light receptors serve as the interlock sensor. When an object breaches the curtain, the light path is changed, shading some of the receptors, changing thereby the state of the light sensor.
Various types of interlock mechanisms have long been used to change the operating state of the machine or to turn off a machine when an operator has to do work in a space where there are moving parts or other hazards to insure that the operator will not be injured when working in the normally guarded space or on the machine. Safe industry practices require that exposed moving parts must be shielded by guards to safely prevent personnel from being injured by coming into contact with hazardous areas of machinery. Needless to say, safety around operating machines has long been a concern in our heavily industrialized world. The design of highly efficient and effective interlock mechanisms that have a high degree of integrity so that they will always act to shut down or otherwise control machines when work is to be done in a space in which there are moving parts and/or other hazards have resulted in continuous development to produce a better interlock. New harmonized European standards and worldwide safety regulations stress the need for proper safety interlocking of machinery.
The integrity of a safety device is defined by its ability to perform its function without failure or default. The greater the risk that exists, then the greater must be the integrity of the safety interlock system required.
There is an all pervasive need to produce an interlock that will not fail. While significant strides have been made, this has not been accomplished, and thus there has long been a need to be able to quickly and efficiently periodically test the many and varied interlocks disposed about machinery to determine whether they have failed or not, and to undertake remedial action if an interlock has failed, so that when they are called upon to act, there is a very high degree of certainty that they will do their intended job. It is to this end that the present invention is directed.
It is not uncommon to enter a plant and observe signs that state in bold letters that "safety is our number one priority" and thus a great deal of attention has been paid to interlock mechanisms to insure that they are located in any area where someone might come in contact with a hazardous part of a machine by opening a guard, but insufficient attention has been paid to testing the interlocks to ensure that they maintain their functionality and integrity. In most of the industrialized countries around the world, there are laws and regulations that require that exposed moving portions or other hazardous sections of machines be covered by locked or movable guards equipped with interlocks to prevent entanglement and injury to the operator by the moving and other hazardous parts of the machine, but unfortunately this is only part of the story if there is not a continuous testing program of the interlocks, since if not tested they may be giving a false sense of security.
Locks on guards have been used for a long time. Such locks will usually not open until powered operation has been interrupted for a predetermined time interval to permit the machine to totally run down or to change its operating state to one eliminating or substantially reducing the hazards of the guarded space. Alternatively, such locks will not open until both powered operation has been interrupted and the moving machine parts have come to rest. The state of rest is generally established by zero speed switches or motion detectors. Sometimes interference devices are inserted into the machinery to assure that motion has been arrested (inserting a stick into the spokes of a wheel). In all of the cases where locks are used, an interlock is incorporated to prevent the machinery from assuming powered operation while the structural guards (barriers) or non-structural guards (light curtains, for instance) are open or out of their protective status. This is where the reliability of interlock mechanisms plays an important and vital role. When called upon to function the interlocks must act to preclude machine start up under powered operation. Interlocks must perform their intended function or else personnel will be placed at risk.
It is very common to observe signs posted around machinery cautioning operators to "shut down the main power to the machine before doing any maintenance or repair work." But even with the proliferation of such signs, the admonitions are often ignored and to a large extent the machine operators rely on the functioning of the interlock systems to prevent their being injured, which further emphasizes the need for a testing system that will insure that the interlock will function when called upon.
Furthermore, even with a well designed interlock system other considerations such as time pressures, production requirements, etc., are dealt with by clever personnel who can and may circumvent the interlock mechanisms by preventing the interlocks from functioning when opening the guards or actually bypassing the interlocks so that the machines will continue to operate while they are working in an unguarded space and with no assurance that the interlock is restored to its functionality afterwards. An interlock that is bypassed has the same functional characteristics as one which is stuck or welded or frozen so that it will not change states. Consequently, the present invention will detect a bypassed or sabotaged interlock as part of its normal testing capability. Once a bypassed interlock is detected, one may either preclude further powered operation of the machine or the structural guards or barriers may be locked into their closed positions until the bypass is removed. Sabotage can never go undetected because it is a long term condition that any regular interlock testing program will uncover. Bypassing, which is a temporary condition, cannot remain unnoticed for longer than one testing interval. Frequent testing will all but eliminate temporary unauthorized bypassing of the interlocks.
It is a gross understatement to state that industry has needed for a long time to quickly, efficiently and periodically test interlocks either automatically or by simple manual manipulation with or without requiring that the guard be opened. Interlocking mechanisms like many other devices are capable of getting stuck, worn out, becoming inoperative, or failing to function for a variety of other reasons that will preclude them from operating successfully when called upon. Unfortunately, interlocks can present a false sense of security to one opening a guard on a machine believing that either the machine will shut down or that it will not restart so that one need not be concerned about beginning to work in the now unguarded space.
Even though there has been awareness of the potential malfunctioning or circumvention of interlocks, there has been no readily available means for quickly, efficiently and repeatedly testing the interlock devices to determine and insure that they are functioning satisfactorily. Conventional available methods for testing existing interlocks include (1) starting the machine and laboriously and manually opening each guard to determine if the machine will shut down or change its operating state as required beginning with one guard and then starting the process all over again with the next guard or (2) sequentially opening the guards with the machine in a shut-down position or the changed operating state and attempt to start the machine or to restore the operating state to determine if the interlocks are functioning properly. That this is time and labor intensive therefore costly and adds unnecessary wear and tear to the machine is self evident. Both of these testing procedures expose operators to a moving machine and other hazards when a defective interlock is being tested.
Regular verification of interlock integrity very seldom takes place because it is time-consuming, interferes with work schedules and may be otherwise difficult to perform, thus leaving interlocks dormant. Since testing of interlocks tends to be neglected, then when they fail due to various causes, the failures remain undetected and the hazards they are supposed to protect against become unprotected or compromised. Also, since interlocks may be remote from the machine operator, extra personnel and coordination is required. Such additional effort and cost provides an additional excuse for not testing or extends verification time intervals. Unfortunately, this is further exacerbated by those personnel that circumvent the interlock mechanism in order to save time, or work in the unguarded space when the interlock mechanism does not function properly, so that they will not be "inconvenienced" by going to the main power or control source to shut the machine off or change its operating state. Operators may consider interlocks a nuisance and will not even report inoperative interlocks. The present invention will uncover temporary bypassing of the interlocks within the testing interval set by a program unit.
It can be appreciated that if repeated testing of the interlock systems can be accomplished to insure proper operation, that the operator will "be saved from himself" in that his reliance on the interlock always functioning correctly may almost be justified. An ongoing quick, and efficient testing system to maximize one's assurance that the interlock system is properly functioning as well as to detect malfunctioning interlocks will go a long way to eliminate or substantially reduce the safety hazards that will occur by malfunctioning interlocks when operators are unwilling to go to the main power or control source and lock out the machine or change its operating state before beginning their work in the hazardous space guarded by the interlock. There has also long been a need to automatically lock a guard in closed position when an interlock malfunctions to insure that personnel will not be injured.
It is the aim of the present invention to provide test mechanisms and systems that will ensure confidence that reliance on interlock systems to perform their tasks when and as received is not misplaced. The invention does this by detecting and identifying which interlocks and their systems are not faulty and which are, and by providing remedial means and actions to those interlocks and systems, and the barrier guards they protect, which have been found faulty. Furthermore, the invention provides the methodology to do the testing, and to apply and then to maintain the remedial actions and means for as long as necessary, without interrupting or disrupting the operation of the machinery. This allows for the scheduling of maintenance, repair or replacement of faulty interlocks and systems at times compatible with the operation of the machinery.
For purposes of this application, the following meaning of terms and expressions is intended here and elsewhere in the application.
Reference to the term "the change of state of an interlock" and similar terms shall be construed to mean a physical change of state of the interlock and the corresponding intended consequential direct or indirect change of state of a machine controlling parameter, most often an electrical parameter, such as, for example, current, voltage, resistance, inductance, impedance, and magnetic field associated with an interlock. For example, and without limitation, a switch of an interlock may be opened or closed, representing physical changes of an interlock producing a change of a machine controlling voltage or current from a first state to a second state.
If opening of a guard is stated or referred to, it shall be construed to mean opening, moving, removing, disrupting, or otherwise breaching of a structural or non-structural barrier guard. Any of these terms, when mentioned in the text, should be understood to be interchangeable where applicable.
A reference to shut down and/or lock out of the machine or machinery shall be construed to mean that, or the alternate of changing the operating state of the machine, machinery and/or its system without shut down or lock out if desired and applicable, and as consequentially or by design substantially or completely reducing the hazards of the interlock guarded space.
Throughout this patent application, failure of the interlock and/or its system shall be taken to mean a failure of the interlock device and/or its system and/or failure of the testing device and/or its system.